Reference may be made to the following U.S. Pat. Nos. of interest: 229,695; 255,914; 376,129; 2,504,057; 2,895,708; 3,223,110; 3,306,570; 4,077,605; 4,286,626.
In many chemical plants specialty process fluids are produced which are intended to be closely regulated by environmental protection desires to prevent release of the process fluids into the atmosphere or into the outside environment. In other instances, the specialty process fluid products may not have an environmental concern but their release into the atmosphere is to be prevented in order to lower the fluid production costs.
Fluid valves are used extensively in chemical plants for controlling the flow of process fluid through pipelines. A particularly troublesome area is the prevention of such specialty process fluids being released into the atmosphere through valve stem packing leakage. The pressure in the pipeline is exerted against the valve stem packing within the valve bonnet and results in the release of small quantities of process fluids containing noxious substances or costly products into the atmosphere.
Sliding stem valves in such a pipeline fluid control application have a requirement that the valve plug and seat be rotatably lapped after assembly to provide the required shut-off. Present sliding stem valves utilize diaphragm devices extending around the valve stem with the valve plug and seat being rotatably lapped by having one end of the diaphragm sealed to the valve stem and the other end of the diaphragm sealed to the bonnet. However, undesired rotation of the valve stem during attempts by an operator to properly seat the valve or to connect the valve stem to an automatic controller, often results in a tearing and destruction of the diaphragm.
Attempts have been made to correct this problem by using anti-rotation devices such as threaded or pinned members which operate satisfactory but this leads to increased valve construction expenses and maintenance, particularly where the anti-rotation devices can be undesirably exposed to the process fluid. Therefore, it is desired to provide a leakproof stem seal for a sliding stem valve which will allow for stem rotation and maintain proper stem sealing with a small number of components.